The present invention generally relates to a technique for cleaning a mechanism for electrostatically attracting an object to be processed and performing a temperature control in a vacuum processing apparatus to be used in a semiconductor-producing process (such as, e.g., sputtering, chemical vapor deposition (CVD), etching or ion plantation).
Recently, problems which had been avoided, have conspicuously appeared in design rules the semiconductor devices.
One example is the issue concerning particles being transferred onto a rear face of a wafer.
Main issues concern the contamination of a washing tank by the particles peeled when the wafers are washed and mutual contamination of wafers, and contamination caused through defocusing in a lithography step.
In order to reduce such transferred particles, it is important to keep the temperature of wafers constant during processing in a processing chamber under a reduced pressure (hereinafter referred to as “processing”) so that an acceptance percentage of chips obtained from a single wafer having a low contact rate may be maintained.
As one of means to enable such a processing, a heating plate having an electrostatically attracting function (hereinafter referred to as “hot plate”) has been heretofore used.
The sputtering apparatus as one of the semiconductor-producing apparatuses has a vacuum processing chamber reduced to a predetermined pressure; and a mechanism for heating and cooling a semiconductor wafer disposed in the vacuum processing chamber.
The temperature control at the time of the film-forming processing is very important from the standpoint of stabilizing the quality of the films; and consideration must be made for the quantity of heat inputted from plasma to the wafer and the transfer of the quantity of heat supplied from the hot plate to the wafer (heat transfer).
In order to satisfy the above state, the heat transfer between the hot plate and the wafer needs to be maximized. As a means to accomplish such heat transfer, it is effective to set the contact areas of the hot plate and the wafer at 1:1.
In the actual processing, problems, such as, “a warp” and “a shape (notch or orientation flat)” of a substrate which have been processed through plural steps, worked accuracy of parts which constituting the apparatus, and a positional precision of a transfer robot are must be considered. It is feared that a metallic film is adhered to an attracting face side of the hot plate, the increase in the particles being transferred, and abnormal discharging occurs, which hinders the delivery of the wafers in the worst case.
Under these circumstances, it is a common practice in such an apparatus that the maximum diameter of the wafer is made greater than the maximum outer diameter of the attracting face of the hot plate.
Further, in order to control the temperature of the wafer during the processing, the quantity of heat inputted from the plasma to the wafer must be considered, and the heat transfer between the wafer and the hot plate needs to be optimized.
In order to improve the heat transfer between the wafer and the hot plate, it is important to increase the contacting face between the wafer and the hot plate. A mechanical clamping, electrostatic attraction or the like can be considered as an ordinary means; and usually, the electrostatically attracting system has been conventionally used from the standpoint of produced particles.
However, increasing the contact areas and the attracting power to enhance the heat transfer leads to the increase in particles being transferred onto the rear face of the wafer as a face for attraction, and it is clear that this problem leads to adverse effect in the yield of semiconductor devices which will become more miniaturized in the future.
Therefore, design considerations are such that particles transferred onto the rear face are to be reduced. However, such designs reduce the attracting areas to the minimum, which is contrary to the concept of increasing the heat transfer.
Under such circumstances, for the purpose of making up for the decreased contact areas (heat transfer), it has been the practice recently for gas to be introduced between a wafer and a hot plate; and heat transfer is carried out therebetween via the gas.
In this case, the processing is carried out through plural process modules in a single apparatus due to the attributes of the sputtering process; and the process temperatures frequently differ in the respective modules. Consequently, the temperature of the wafer immediately after it is transferred into the module differs from the set temperature (process temperature) of the hot plate, so that frictional electrification occurs at the time of electrostatic attraction, and a transfer error is caused by the poor removal of the wafer. Accordingly, the insulating resistance value of the attracting face needs to be set in a Johnson-Rahbeck range.
In addition, because the temperature of the wafer needs to be raised to the processing temperature until the sputtering, the electrostatically attracting system has to be of a bipolar specific.
The semiconductor wafer is repeatedly processed by various steps (such as, exposure, film formation, etching, washing, etc.). During the processings, attachment of an electroconductive material on the rear face of the wafer cannot be avoided.
Furthermore, organic materials (such as, Low-k materials) have been recently used as semiconductor constituting materials. In the case of such a material, when the wafer is to be processed with the hot plate placed in an apparatus module, the electrostatic attracting force between the wafer and the hot plate is intentionally increased. Thus, it is easily presumed that an electroconductive material at the rear face of the wafer is easily transferred to the attracting face of the hot plate.
Meanwhile, when the chamber is baked on starting up the module after maintenance in the open atmosphere, the electroconductive material is contained in a material peeled from constituting parts (adhesion-preventing plate, chamber wall).
In this way, the electroconductive material transferred onto the hot plate forms a low-resistance layer on the outermost face of the hot plate.
Because such a low-resistance layer exhibits a resistance lower than a resistance of an insulating layer (hereinafter referred to as dielectric layer) of the attracting face of the hot plate, in the case of the attracting force due to the Jonson-Rahbeck force utilizing inducing charges onto the outermost face of the dielectric layer by controlling the resistance value in order to flow minute electric currents between ESC electrodes and between the wafer and the ESC electrodes depend on the resistance of dielectric layer, the electroconductive material shortcuts between ESC electrodes, and a condenser circuit is not formed between the ESC electrodes.
Therefore, lines of electric force between the wafer and the ESC electrodes terminate at the ESC electrodes; and consequently, no attracting force appears because no charging polarization takes place at the surface of the wafer.
Meanwhile, when the sectional structure of the attracting face of the hot plate to be used in this kind of apparatus is observed, it is an embossed structure to minimize the particles transfer onto the rear face of the wafer.
The directly contacting face to the wafer comprises top faces of projections, at which an implementing electrostatically attracting force operationally needed is obtained.
On the other hand, although the attracting force is generated even at bottom portions of depressions of the attracting face of the hot plate, it is very weak (and it is generally called a “spatial force”) because the force is inversely proportional to the distance up to the wafer (and a potential between the wafer cannot be specified).
When a low-resistance layer is attached to this embossed attracting face of the hot plate, it is difficult to remove the layer even by using WET washing at the outside because the sectional shape is very complicated.
As a result, the electrostatically attracting force is not generated or lowered so that inconveniences occur such that the temperature of the wafer not rising within a predetermined time period, and the temperature of the wafer not being able to be controlled to a constant level during a plasma processing, etc.
Because the low-resistance layer formed on the attracting layer depends on the user's processing (such as, a carried amount, the temperature of the hot plate, the processing time periods, etc.) and there are large variations among the apparatuses or the modules, it is difficult to confirm the attached state.
As mentioned above, the electroconductive material carried into the vacuum processing apparatus with the wafer needs to be removed in order to maintain a stable attracting force.
Due to such problems, a cleaning method is heretofore proposed, which performs steps of plasma etching by applying a high-frequency electric power to an attracting electrode of an electrostatic chuck, placing a substrate on this electrostatic chuck and carrying out the substrate having been placed on the electrostatic chuck at the substrate-placing step (For example, see JP-A 2002-280365).